With the rise of national income, Korea has become world s seventh largest paper (including publications, newspapers, publishing cardboards, kraft paper, bulk paper, etc.) consumer and at the same time world s ninth largest paper producer. However, it imports 100% of pulp, which is used to produce paper, from abroad. In an effort to meet the need for pulp materials, countries with poor forest resources like China, the Middle East and India are developing herbaceous agricultural wastes or bamboos into pulp materials, in the national level. Even the sugar cane dregs discarded after sugar making are developed into pulp materials.
A new pulp material should be developed because fostering pulp industry results in destruction of forest resources. To do so, cellulose present in a variety of plants should be processed and treated to improve their value as paper materials. Countries rich in forest resources separate fibrous cellulose from wood to produce paper pulp and dissolving pulp. Thus, over 90% of pulp produced across the world is made from wood.
However, with a plant distribution inappropriate for pulping and with a dearth of forest resources, Korea has to find a new strategy.
Corn grown in farms is used as food. But, cornstalks are mostly discarded even without being used as fodder. In the light of resources utilization and farmers income augmentation, cornstalks need to be processed and treated to be useful for pulp or other materials, for example, as in development of the Korean paper.
Each year, 750 million tons of cornstalks are produced worldwide. In the U.S. alone, some 150 million tons of cornstalks are produced a year. But, cornstalks are not used in pulping and paper-making industries, although 30 to 70% of them are adequate for paper making.
Pulps can be largely classified into mechanical pulp, semichemical pulp and chemical pulp, depending on the pulping process. Mechanical pulp is manufactured by dissolving wood by mechanical grinding in the presence of water. Acicular trees with long fiber length, such as spruce, fir, pine and black pine, are pulped by this method. Semichemical pulp is manufactured by steaming wood with a neutral sulfite solution and dissolving it through mechanical treatment. Light and soft trees, such as poplar, willow, linden tree, beech, oak, alder tree and ash tree, are pulped by this method. Chemical pulp is manufactured by adding a mixture solution of sulfurous acid and acidic sulfite to a fibrous material and digesting it. Trees with low resin content are manufactured into chemical pulp because of convenience in chemical treatment.
Usually, mechanical pulping requires less facility cost offers better yield and can be produced at a lower cost, compared with chemical pulp. Also, mechanical pulp is better than chemical pulp in view of pollution. However, mechanical pulp has worse quality than chemical pulp. Thus, if both quality and price are required, it is common to mix the two to obtain wanted pulp. With the improvement of mechanical pulp, basically derived from refiner mechanical pulp (RMP), now it can have properties comparable to those of chemical pulp. This mechanical pulp can replace all or part of chemical pulp. For example, Canadian Patent Nos. 1071805, 1145106 and 1145107 disclose methods for manufacturing mechanical pulp useful as replacement of chemical pulp. In the methods of these patents, thermal mechanical pulp (TMP), refiner mechanical pulp (RMP) or thermal chemical mechanical pulp (TCMP) that has passed through a refining process is treated with an sodium sulfite, a chemical for digesting, or mixed with the solution. Then, the treated pulp is further refined (an optional process) by digesting under applied pressure. U.S. Pat. No. 4,502,918 discloses a pulping method of treating wood particles with a sodium sulfite solution, digesting and refining the particles and separating pulp from the particles. French Patent No. 2544757 discloses a method of producing pulp from bagasse and bamboo. This method comprises at least two digesting processes. A digesting agent is added prior to each digesting process. This patent also comprises a blow-down process in between the digesting processes for separation of fascicular fibers.
Referring to prior researches related with cornstalks, U.S. Pat. No. 1,639,152 (1927), which was patented in the situation where quantitative experimentation was unavailable, discloses a pulping process which comprised separating fibroid material from cornstalks by microbial fermentation and extracting pulp using soda, lime and sulfite for use as lumber substitutes, wall boards, insulating materials, and so forth. Although the patent simply teaches that cornstalk can be digested and dissolved by such chemicals as soda, lime, sulfite, and so forth to make paper for newspapers, it does not mention anything about specific composition of the cornstalk digesting solution, amount of addition thereof, digesting temperature or digesting time. U.S. Pat. No. 1,845,487 discloses a process of preparing cellulose by digesting and dissolving plants with a small lignin content and a high pentosan (a pentose) content with dilute sulfuric acid or with sulfuric acid and a pressure of 10 pounds, and a pulping process of heating and pressing chipped or powdered cornstalks with a 1% sulfuric acid solution to remove water-soluble materials. U.S. Pat. No. 5,944,953 discloses a pulping process of cornstalks or straw encompassing both mechanical and chemical methods. It mentions using soda (NaOH), lime soda (CaO2+NaOH) and neutral sulfite (Na2SO2+NaOH). Although not specifying the addition amount, it describes pulp making by refining cornstalks with 10-15 wt % of potassium hydroxide (KOH) and 1-5 wt % of potassium sulfite (K2SO3), based on the dry weight of cornstalk. Russian Patent No. 213995 describes a general herbaceous pulping process. This patent mentions nothing about solution composition, temperature or time of the digesting/dissolving process.
Thus, development of a method capable of effectively producing pulp from cornstalks is required.